This invention relates to a method for transferring a developing layer having a visible image thereon from a developing medium to a heat sealing sheet.
There has been conventionally known an image forming apparatus using a photosensitive and pressure-sensitive recording medium coated with microcapsules mainly encapsulating dye precursor, photocurable resin and photopolymerization initiator and a developing sheet coated with developer agent capable of reacting with the dye precursor to color the dye precursor. In this type of image forming apparatus, as described in Japanese Unexamined Published Patent Application No. 61-173981, the photosensitive and pressure-sensitive recording medium is exposed to light in accordance with an image information to photocure the photocurable resin encapsulated in the microcapsules, and then is superposed over the developing sheet under pressure to thereby rupture those microcapsules which have not been exposed to light. As a result, the dye precursor issued from the ruptured microcapsules is reacted with the developer agent on the developing sheet to be colored, that is, a color image is formed on the developing sheet.
In this type of image forming apparatus, however, a color image can be formed on a specifically-produced sheet such as a developing sheet coated with the developer agent, but can not be formed on any kind of an image supporting medium such as a plain paper such as a post card, cloth, plastic film or the like. If it is daringly tried to form a color image on the medium such as a post card, cloth or the like, it is required to paste the developing medium having the color image thereon on the medium after the color image is formed on the developing medium. In this case, the image supporting medium on which the color image is finally supported is more increased in thickness and weight. This is inconvenient for a practical use.
In view of the above disadvantage, the applicant of this application has proposed the following method for forming a color image on an image supporting medium such as a post card, cloth, a plastic film or the like, as described in Japanese Patent Application No. 63-31455. In this method are used two types of image forming media, one of which comprises a developing medium having a substrate and a developer agent layer (image forming layer) on which a color image is formed, and the other of which comprises a heat sealing sheet including a sheet substrate and a thermoplastic resin layer coated on the sheet substrate. Both the surfaces of the developing medium having the developer agent layer containing the color image thereon and the thermoplastic resin layer of the heat sealing sheet are contacted with each other and supplied with heat and pressure, so that the developing medium is attached to the heat sealing sheet with thermoplasticity of the thermoplastic resin. After being cooled substrate of the developing medium is exfoliated from the developing medium attached to the heat sealing sheet. As a result, only the developer agent layer (image forming layer) is transferred to the heat sealing sheet. Thereafter, the heat sealing sheet to which the image forming layer is transferred is attached to an image supporting medium such as a post card, cloth, plastic film or the like, whereby a color image is finally supported on any kind of medium such as the post card, cloth, plastic film or the like.
In this method, in addition to the image forming layer, the heat sealing sheet is also attached to the image supporting medium, so that flexibility of the image supporting medium is degraded due to the attachment of the sheet substrate thereto. Such a degradation of flexibility of the image supporting medium restricts the types of the image supporting medium to be used. For example, cloth which is required to be flexible can not be used as an image supporting medium in such a method. In order to overcome such a disadvantage, in Japanese Patent Application No. 63-147805, Japanese Utility Model Application No. 63-84914 and Japanese Utility Model Application No. 63-84915, there has been proposed a method in which the sheet substrate of the heat sealing sheet is also exfoliated from the image supporting medium in consideration of the relationship in adhesion among the sheet substrate of the heat sealing sheet, the thermoplastic resin, the developer agent layer (image forming layer), and the image supporting medium. This method has the same process for transferring the image forming layer from the developing medium to the heat sealing sheet as that of the foregoing method.
However, when the substrate of the developing medium is a paper, it is difficult to separate only the substrate from the developing medium which is attached to the heat sealing sheet with heat and pressure. For example, there is a possibility that the separation is not made between the substrate and the developer agent layer of the developing medium, but between the sheet substrate and the thermoplastic resin layer of the heat sealing sheet due to the relationship between the adhesions thereof.